The technical field of the invention is capillary electrophoresis.
Capillary electrophoresis (CE) has been gaining increasing utility for conducting chemical and biochemical operations. It provides many benefits including substantial savings in time of analysis, cost of analysis, laboratory space required for performing the analysis, automation and high throughput. These benefits are due in great part to miniaturization and the alleviation of associated human factors, e.g., labor costs, costs associated with operator error, and general inconsistencies from individual to individual and overall human operation.
Due to factors such as convenience, cost and efficiency, plastic materials have become very attractive for use in the field of CE. For instance, conventional molding techniques can be used to produce large numbers of disposable plastic devices, each having precise and intricate features such as microchannel networks and reservoirs. Plastic films can also be efficiently extruded into laminates containing electrophoretic channels. Various plastics or polymers can and have been used with the molds and films mentioned above. These include polymethacrylates and other acrylics, polycarbonates, polydimethylsiloxanes, and polyalkenes, among others. The problems with each however, are complex surface chemistries accompanied with variations in wall surface charge physical and chemical configuration and microstucture. These chemistries and surface charges tend to aggravate sample adsorption to the capillary walls and generate non-uniform electroosmotic flow. Because adsorption results in skewed peaks and/or no analyte migration while non-uniform electroosmotic flow causes reduced separation resolution, reliable and consistent results have been difficult to obtain.
EOF is highly dependent upon both Zeta potential and viscosity at the vicinity of a solid micro-channel wall. The Zeta potential is the potential at the shipping plane (surface of shear) between the charged or ionized surface and the electrolyte solution or buffer, depending on the surface charge density, the buffer or medium composition and the pH. This effect is present with a variety of substrates. For example, where a conventional silica capillary is used for CE, EOF is enhanced due to the negatively charged inner walls of the capillary. These walls are dominated by silanol groups that attract a diffuse layer with excess positive ions from the electrolyte buffer. As the mobile excess positive ions in the diffuse layer flow toward the cathode under the influence of the electrical potential, the bulk solution is also dragged to the same direction.
Currently there are several ways to partially or fully control EOF and adsorption, including buffer changes and additives, use of organic solvents, adsorption of neutral and/or charged macromolecules (including surfactants) to the wall, chemically bonded phases and the like. See, for example, U.S. Pat. Nos. 4,68,201, 4,690,749, 4,865,707, 4,931,328, 5,112,460, which are incorporated herein by reference. The underlying idea is to modulate the nature of the charges on the wall to substantially reduce charged entities. Each of these methods has deficiencies and may not provide the desired reduction in EOF, while still providing other desired surface properties for the performance of CE.
Methods and devices are provided employing norbornene based polymer surfaces for performing capillary electrophoresis. Substantially saturated neutral poly (norbornene) homo- and copolymers are employed as the surface for microchannels in which ions are moved under the influence of an electric field. Improved separations and resolutions of mixtures, particularly nucleic acid mixtures, are achieved under comparable conditions using other microchannel surfaces, without the need to pretreat the surface to avoid EOF.